Geophysics and geochemistry of iron in the Earth's core

The high pressure and temperature behavior of Fe and Fe-rich alloys was investigated in a diamond anvil cell using a suite of synchrotron x-ray diffraction and spectroscopy techniques with the goal of expanding our understanding of the geophysics and geochemistry of the Earth's core.; The elastic anisotropy of a hexagonal close-packed Fe sample at 52 GPa and room temperature was studied using radial x-ray diffraction and inelastic x-ray scattering spectroscopy for testing theory and comparison with seismic observations. Incorporation of the textural analysis with the inelastic x-ray scattering spectroscopy and nuclear resonant inelastic x-ray scattering results allow for a more accurate determination of the bulk elastic parameters. We found that the nature of the velocity anisotropy of Fe at 52 GPa was consistent with previous radial x-ray diffraction studies with the maximum velocity at 45° to the compression axis, but the magnitude of the anisotropy was much lower (approximately 3% difference between the maximum and minimum compressional wave velocities) and may not be resolvable above experimental uncertainty. We have developed a comprehensive and robust approach which can be extended to any P-T with improvements in the efficiency of inelastic x-ray measurements.; Fe with 5wt%, 15wt%, and 20wt% Ni was studied to 55 GPa, 62 GPa, and 72 GPa respectively at temperatures up to ∼3000 K. Ni stabilizes the face-centered cubic phase to lower temperatures and higher pressure, and this effect increases with increasing pressure. Extrapolation of our experimental results suggests that the stable phase at inner core conditions is hexagonal close-packed, although if the temperature at the inner core boundary is higher than ∼6400 K, a two phase outer region may also exist. Comparison to previous laser-heated diamond anvil cell studies demonstrates the importance of kinetics even at high temperatures highlighting the importance of reversing transitions to establish phase boundaries.; The nuclear resonant x-ray scattering of FeHx was measured to 52 GPa at ambient temperature. Coupled with hydrostatic x-ray diffraction data, the partial phonon density of states measured by nuclear resonant inelastic x-ray scattering provides information on sound velocities and the Fe sublattice contribution to thermodynamic parameters. (Abstract shortened by UMI.)...